Combustion influences on natural abundance nitrogen isotope ratio in soil and plants following a wildfire in a sub-alpine ecosystem

摘要

This before-and-after-impact study uses the natural abundance N isotope ratio (tp#eN) to investigate the effects of a wildfire on sub-alpine ecosystem properties and processes. We measured the p#eN signatures of soil, charred organic material, ash and foliage in three sub-alpine plant communities (grassland, heathland and woodland) in south-eastern Australia. Surface bulk soil was temporarily enriched in p#eN immediately after wildfire compared to charred organic material and ash in all plant communities. We associated the enrichment of bulk soil with fractionation of N during combustion and volatilization of N, a process that also explains the sequential enrichment of p#eN of unburnt leavesiu >iu ashiu >iu charred organic material in relation to duration and intensity of heating. The rapid decline in p#eN of bulk soil to pre-fire values indicates that depleted ash, containing considerable amounts of total N, was readily incorporated into the soil. Foliar tp#eN also increased with values peaking 1iu year post-fire. Foliar enrichment was foremost coupled with the release of enriched NH into the soil owing to isotopic discrimination during volatilization of soluble N and combustion of organic material. The mode of post-fire regeneration influenced foliar p#eN enrichment in two species indicating use of different sources of N following fire. The use of natural abundance of p#eN in soil, ash and foliage as a means of tracing transformation of N during wildfire has established the importance of combustion products as an important, albeit temporary source of inorganic N for plants regenerating after wildfire.